The role of extracellular matrix protein 1 in human skin.

Extracellular matrix protein 1 (ECM1) was first identified in 1994 as an 85-kDa glycoprotein secreted by a mouse osteogenic stromal cell line. Subsequently, the human homologue has been found to regulate endochondral bone formation, and to stimulate proliferation of endothelial cells and induce angiogenesis. However, a role for ECM1 in skin physiology and homeostasis has also emerged. Specifically, in 2002, loss-of-function mutations in the ECM1 gene were discovered to be the cause of the rare autosomal recessive genodermatosis, lipoid proteinosis. This inherited disorder is characterized clinically by skin and mucosal infiltration and scarring and histologically by disruption/duplication of basement membrane and widespread deposition of hyaline material in the dermis. Moreover, other recent studies have identified circulating autoantibodies against the ECM1 protein in most patients with lichen sclerosus, a common chronic inflammatory condition that shares some clinicopathological features with lipoid proteinosis. ECM1 thus serves as a target antigen in both an inherited and an acquired skin disorder. Within the epidermis, ECM1 has a role in the control of keratinocyte differentiation. Within the dermis, ECM1 binds to the major heparan sulphate proteoglycan, perlecan. In this way, ECM1 may act as a "biological glue" in the dermis, helping to regulate basement membrane and interstitial collagen fibril macro-assembly and growth factor binding. ECM1 may also have a role in other acquired skin disorders and physiological skin changes including scarring, wound healing and skin ageing, although this remains to be determined.